Fermi GRBs in the plane E_pi –E_iso. The black symbols show 43 GRBs with a redshift and the black solid lines show the corresponding best fit E_pi – E_iso relation with its two sigma limits. Black circles are 34 GRBs detected simultaneously by Fermi/GBM and Swift/BAT. Black triangles are nine GRBs detected simultaneously by Fermi/GBM and another positioning instrument (usually Fermi/LAT). The purple circles indicate GRBs whose redshift has been measured with the emission lines of the host galaxy. The green and red lines show the possible positions of GRBs without a redshift when they are placed at distances ranging from z = 0.34 (leftmost point) to z = 4.35 (rightmost point). Red lines indicate GRBs that are beyond the two sigma limit of the E_pi – E_iso relation at any redshift. The dotted blue lines show the best fit E_pi – E_iso relation of Nava et al. (2012) with its two sigma limits. The dashed blue lines show the best fit E_pi – E_iso relation of Amati (2006) with its two sigma limits.